1. Field of the Invention
The invention relates to a process for the thermal treatment of dustlike and/or finely divided solids which arise in the purification of flue gases.
2. Discussion of the Background
It is known that polychlorinated hydrocarbons form in the incineration of refuse in the presence of an oxygen excess. Thus Olie, K. et al. reported in Chemosphere 1977, 6, 455 on polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in dusts from electrostatic precipitators of domestic refuse incineration plants.
Hagenmaier, H. et al. in Environ. Sci. & Technol 987, 21, 1080 report that the limitation of oxygen in the catalytic dechlorination at 300.degree. to 400.degree. C. leads to substantial destruction of PCDDs and PCDFs.
This finding is utilized in the device described in DE-A 3,703, 984 for the destruction of halogenated aromatic compounds. The thermal treatment takes place here in a drum closed off from the external atmosphere and with no continuous flow through it. The fly ash to be treated is transported in axial and radial direction through the drum by means of panels mounted on a rotatable shaft. During this, the transported material is compressed and the drum outlet as a consequence is occasionally blocked, which leads to interruption of operation. Sealing the drum, in particular the bearing, is problematic. The oxygen in the air entering as a result of the leakage leads to the reverse reaction, i.e. to reformation of the chlorinated hydrocarbons to be destroyed. The heat required for the fly ash treatment is supplied via the drum wall in this known process; in this case, for an effective treatment temperature of up to 400.degree. C., wall temperatures of up to 600.degree. C. are required. At this high temperature, the chlorine formed in the treatment produces corrosion of the device and low-melting-point salts present in the fly ash can form caking which can lead to jamming or choking of the plant. In practice, the drum must be provided with a vapor extraction device, the filter of which regularly plugs.